要求C语言编写，实现C8051F020通过UART于PC实现数据交换，单片机使用外部22.1184MHz晶振。要求实现的功能：Uart驱动程序，包括初始化、波特率设置，单字节发送接收、字符串发送接受。 程序运行时向PC机发送字符串；接收到PC机的数据后，再将该数据发送回PC机。-Requirements written in C, to achieve C8051F020 UART to PC through data exchange, the microcontroller using an external 22.1184MHz crystal. Required to achieve the function: Uart driver, including initialization, baud rate, single-byte transmit and receive, send the string accept. The program runs to the PC sends the string　receives the data to a PC, then the data is sent back to the PC.